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SIAH-1 interacts with CtIP and promotes its degradation by the proteasome pathway

Antonia Germani1, Audrey Prabel, Samia Mourah

  • 1Laboratory of Vascular Biology and Gene Therapy, Centro Cardiologico Fondazione-IRCCS, Via Parea 4, 20138 Milano, Italy.

Oncogene
|December 5, 2003
PubMed

Insights

The study reveals that SIAH-1 (seven in absentia homolog 1) interacts with CtIP (CtBP-interacting protein), but its role in p21(Waf-1/Cip-1) gene induction is not dependent on CtIP degradation. This finding challenges previous assumptions about the mechanism of SIAH-1-mediated gene regulation.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Biochemistry

Background:

  • SIAH-1 and SIAH-2 are highly conserved E3 ubiquitin ligases.
  • SIAH-1 is implicated in apoptosis and tumor suppression, with its expression induced by p53 and p21(Waf-1/Cip-1).
  • Overexpression of SIAH-1 in MCF-7 cells correlates with apoptosis, mitotic changes, and p21(Waf-1/Cip-1) induction.

Purpose of the Study:

  • To investigate the interaction between SIAH-1 and CtIP.
  • To elucidate the role of this interaction in the regulation of p21(Waf-1/Cip-1) gene transcription.
  • To determine if CtIP degradation mediates SIAH-1-induced p21(Waf-1/Cip-1) expression.

Main Methods:

  • Two-hybrid screening to identify SIAH-1 interacting proteins.
  • In vitro and in vivo association assays for SIAH-1 and CtIP.
  • Ubiquitin-proteasome pathway analysis.
  • Reporter gene assays to measure p21(Waf-1/Cip-1) promoter activity.

Main Results:

  • CtBP-interacting protein (CtIP) was identified as a SIAH-1 interacting protein.
  • SIAH-1 associates with CtIP both in vitro and in vivo, leading to CtIP degradation via the ubiquitin-proteasome pathway.
  • SIAH-1 induced p21(Waf-1/Cip-1) transcription in Jurkat-T cells.
  • A SIAH-1 mutant (SIAH-1DeltaN) that interacts with CtIP but does not degrade it also induced p21(Waf-1) promoter activity, suggesting CtIP degradation is not the mechanism.

Conclusions:

  • SIAH-1 interacts with CtIP and promotes its degradation.
  • The induction of p21(Waf-1/Cip-1) transcription by SIAH-1 is independent of CtIP degradation.
  • This suggests alternative mechanisms for SIAH-1-mediated transcriptional regulation.

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